Direct isolation of Francisella spp. from environmental samples

Abstract

Aims: To develop a selective medium for isolation of F. tularensis, F. novicida and F. philomiragia from environmental samples.

Methods and results: A selective media, cysteine heart agar with 9% chocolatized sheep blood, containing polymyxin B, amphotericin B, cyclohexamide, cefepime and vancomycin (CHAB-PACCV) was developed and evaluated for growth of Francisella spp. No differences were observed in recovered colony forming units (CFUs) for F. tularensis, F. novicida and F. philomiragia on CHAB-PACCV vs nonselective CHAB. Growth of non-Francisella species was inhibited on CHAB-PACCV. When environmental samples were cultured on CHAB and CHAB-PACCV, only CHAB-PACCV allowed isolation of Francisella spp. Three new Francisella strains were isolated directly from seawater and seaweed samples by culture on CHAB-PACCV.

Conclusions: CHAB-PACCV can be used for direct isolation of Francisella spp from environmental samples.

Significance and impact of the study: Francisella spp. show a close association with environmental sources. Future utilization of CHAB-PACCV for isolation of Francisella spp. directly from environmental samples should prove valuable for investigating outbreaks and human infections attributed to environmental exposure.